Not sure. We haven't done much on a quantum level yet (1st year Physics at Sheffield).

I'm thinking of eddy currents: when current flows through the voice coil, it creates a magnetic field, which must disturb that of the permanent magnet.
For a perfectly conducting magnet, huge eddy currents would flow in order to oppose these changes, and the magnetic field would hold rigid.
For some material that doesn't conduct perfectly, its magnetic field is dented inwards, as the eddy currents don't fully compensate.
Copper demodulation rings are often used in higher-end speakers to ensure greater eddy current flow, to keep the magnetic field more rigid. These are usually found on Ferrite magnets: I'm told Neodymium doesn't need it, as its a much better conductor.

A "rigid" magnetic field is desirable for HiFi: it reduces distortion. For guitar, its all about which subjectively is better.
I'd infer that AlNiCo is a relatively poor conductor of electricity, giving it the legendary "smooth" sound.

So, speaker design is the battle of the eddies?
Indeed, it's entirely subjective. It's just because I'm a guitarist that I'm an alnico buff. And even then many guitarists prefer a harsher sound.

In guitars a mahogany body and a maple top work against each other, causing frequencies to cancel, to which the smoothness (in sound) of this wood combo is attributed.
So I would expect alnico smoothness to be based upon the filtering of frequencies also.

Think about the relative conductivities of different magnets, and what happens when current flows through a voice coil.

Are you talking about magnetic conductivity (permeability) or electrical conductivity? Alnico is a metal and conducts well, NIB and ferrite are ceramics - poor conductors. So is the issue the relative susceptibility of each magnet to having eddy currents induced in them, thereby altering their field, hence distortion? If this is the case, alnico being a conductor is most susceptible to induced eddy currents and probably has the most distortion, explaining why electric guitarists like them.

Are you talking about magnetic conductivity (permeability) or electrical conductivity? Alnico is a metal and conducts well, NIB and ferrite are ceramics - poor conductors. So is the issue the relative susceptibility of each magnet to having eddy currents induced in them, thereby altering their field, hence distortion? If this is the case, alnico being a conductor is most susceptible to induced eddy currents and probably has the most distortion, explaining why electric guitarists like them.

This discussion also makes me wonder if all the "field coils" in uber-high-end drivers is really all hype? There is no room temperature (read non superconducting) electromagnet that can achieve the same field strength of a NIB magnet. Why bother unless you want some sort of active field strength adjustment or something like that? Are there other benefits to field coils that I am unaware of other than having to provide yet another high current regulated DC power supply for the coils?

global cobolt production AlNiCoCobalt Production by Country (Metric tons, cobalt content)
And from Wiki
The Second Congo War, beginning in 1998, devastated the country and is sometimes referred to as the "African world war" because it involved nine African nations and some twenty armed groups.[4] Despite the signing of peace accords in 2003, fighting continues in the east of the country. There, the prevalence of rape and other sexual violence is described as the worst in the world.[5] The war is the world's deadliest conflict since World War II, killing 5.4 million people since 1998.[6][7] The vast majority died from conditions of malaria, diarrhea, pneumonia and malnutrition.[8]

global cobolt production AlNiCoCobalt Production by Country (Metric tons, cobalt content)
And from Wiki
The Second Congo War, beginning in 1998, devastated the country and is sometimes referred to as the "African world war" because it involved nine African nations and some twenty armed groups.[4] Despite the signing of peace accords in 2003, fighting continues in the east of the country. There, the prevalence of rape and other sexual violence is described as the worst in the world.[5] The war is the world's deadliest conflict since World War II, killing 5.4 million people since 1998.[6][7] The vast majority died from conditions of malaria, diarrhea, pneumonia and malnutrition.[8]

That's shocking, isn't it? Everyone should write to their president or PM to do something about it, because THEY (the legislators) have the power and responsibility to do something about it, although they deny it.

Anyway...this thread is quite interesting, thanks to the previous posters. I used to think that speaker distortion was a mechanical thing: the cone and the paper going haywire. As a home recordist I can't put my neighbors through pushing my speakers to distortion anyway. But now I understand that speaker distortion is also in the interaction between magnet and coil. Would it then be possible to control or induce speaker distrortion electrically, that is, vary the susceptibilty of the speaker to distortion, so that it distorts at lower volumes?